I've seen a couple of threads on the relative advantage of speed vs senses for increasing initiative. I did a quick test starting a priest (since they should be fast) and did 4 different configurations, one with no increase in either speed or senses, one with increases in one but not the other, and finally one with the same increase in both. I found that there was no differnce between the effects from speed of senses, they were identical. Now this was based on adding 17 skill points to the stats, which gave an increase in init of 3 points per 17 points. My guess is that you get one point of init for every 5 points of either speed or senses. I haven't confirmed that however.